An easy way to find you api token is to look it up in the response of the webapp after logging in at the BEEP app.
In most web browsers you can use the development tools -> Network traffic sidebar to find your api_token: In the screenshot below, you'll see a preview of the result of the /authenticate call that contains your api_token.
This is the token that must be provided as a Header: Authorization: Bearer api_token to all API calls marked with Requires authentication.
BEEP Acceptance environment: test.beep.nl
NB: The API documentation contains sample requests to the BEEP acceptance environment (test.beep.nl). You can use https://test.beep.nl/api to test API calls in the BEEP acceptance environment. First create a test account for the acceptance environment in the app is placed at https://test.beep.nl/webapp. Data stored in the acceptance environment is purged every now and then at major version updates.